Sexual conflict reduces offspring fitness in zebra finches

Parental care is often costly; hence, in sexually reproducing species where both male and female parents rear their offspring (biparental care), sexual conflict over parental investment can arise. Such conflict occurs because each care-giver would benefit from withholding parental investment for use with another partner, leading to a reduction in the amount of care given by one parent at the expense of the other. Here we report experiments to explore the prediction from theory that parents rearing offspring alone may provide greater parental investment than when rearing offspring together with a partner. We found that when the number of offspring per parent, and hence the potential workload, were kept constant, offspring received a greater per capita parental investment from single females than from both parents working together, and that males reared by single mothers were more sexually attractive as adults than their biparentally reared siblings. This difference between single- and two-parent families is due to a reduction in care provided by females when they care together with a male, rather than laziness by males or differences in the begging behaviour of chicks, supporting the claim that sexual conflict in biparental care can reduce the quality of offspring raised.     

Animal behavior: male parenting of New Guinea froglets

Male parental care is exceptionally rare in nature, although one of the most fascinating aspects of New Guinea's biodiversity is the evolution of male care in the frog family Microhylidae. Here I report a new mode of parental care: transport of froglets by the male parent, which was recently discovered in two species of microhylid frogs from the mountains of Papua New Guinea. As the offspring jump off at different points, they may benefit from reduced competition for food, lower predation pressure and fewer opportunities for inbreeding between froglets, which may explain why this unusual form of parental care evolved.     

Palaeontology: parental care in an ornithischian dinosaur

Crocodilians and birds show extensive parental care of their young, but whether this behaviour evolved independently in these two groups of living archosaurs is unknown - in part because features of parenting among related fossil groups such as dinosaurs are unclear. A dramatic specimen of the small ornithischian dinosaur Psittacosaurus sp. (Dalian Natural History Museum D2156) from Liaoning in China reveals a single adult clustered with 34 juveniles within an area of 0.5 square metres, providing strong evidence for post-hatching parental care in Dinosauria.     

Pre-social benefits of extended parental care

The evolution of helping, in which some individuals forfeit their own reproduction and help others to reproduce, is a central problem in evolutionary biology. Recently proposed insurance-based mechanisms rely on a pre-existing life history with a long period of offspring dependency relative to the short life expectancies of adult carers: a lone mother's offspring are doomed if she dies young, whereas after a helper dies, other group members can finish rearing the offspring. A critical question, however, is how this life history could evolve in ancestral non-social populations, as offspring survival would then depend on a single, short-lived carer. Here, we resolve this paradox by focusing on the extended parental care inherent in prolonged dependency. We show experimentally that in non-social wasps, extended care can significantly reduce the impact of interspecific parasites. Under extended care, offspring are less vulnerable by the time they are exposed to parasites, and costs of parasitism are reduced because mothers have the option to terminate investment in failing offspring. By experimentally simulating aspects of extended care in a species where it is lacking, we demonstrate that neither benefit requires specialized behaviour. Such benefits could therefore offset the disadvantage of prolonged dependency in non-social species, thereby facilitating the evolution of helping.     

Sustainable trophy hunting of African lions

In most species, sport hunting of male trophy animals can only reduce overall population size when the rate of removal of males is so high that females can no longer be impregnated. However, where males provide extensive paternal care, the removal of even a few individuals could harm the population as a whole. In species such as lions, excessive trophy hunting could theoretically cause male replacements (and associated infanticide) to become sufficiently common to prevent cubs reaching adulthood. Here we simulate the population consequences of lion trophy hunting using a spatially explicit, individual-based, stochastic model parameterized with 40 years of demographic data from northern Tanzania. Although our simulations confirm that infanticide increases the risk of population extinction, trophy hunting could be sustained simply by hunting males above a minimum age threshold, and this strategy maximizes both the quantity and the quality of the long-term kill. We present a simple non-invasive technique for estimating lion age in populations lacking long-term records, and suggest that quotas would be unnecessary in any male-only trophy species where age determination could be reliably implemented.     

Decisions about parental care in response to perceived paternity

Evolutionary ecologists are attempting to explain how parents make behavioural decisions about how much care to provide to their young. Theory predicts that when genetic relatedness to young is decreased by cuckoldry, for example, parents should reduce their care in favour of alternative broods that provide greater reproductive success. Experimental manipulation of perceived paternity has been used to test the theory, but such studies have generated mixed results. Some manipulations can fail to alter a parent's perceived paternity, whereas others may directly affect parental behaviour when, for instance, the manipulation involves capturing the parent. No study has demonstrated parental care adjustment in a manner uncomplicated by experimental design or life history correlates. Here I test the theory using the fact that nest-tending parental male bluegill sunfish (Lepomis macrochirus) can assess their paternity using both the visual presence of parasitic cuckolder males during spawning, and olfactory cues released by newly hatched eggs. By manipulating both types of cues I show that parental males dynamically adjust their parental care, favouring broods that are apparently most closely related. These results confirm the importance of genetic relatedness in parental care decision-making.     

Parental investment by skin feeding in a caecilian amphibian

Although the initial growth and development of most multicellular animals depends on the provision of yolk, there are many varied contrivances by which animals provide additional or alternative investment in their offspring. Providing offspring with additional nutrition should be favoured by natural selection when the consequent increased fitness of the young offsets any corresponding reduction in fecundity. Alternative forms of nutrition may allow parents to delay and potentially redirect their investment. Here we report a remarkable form of parental care and mechanism of parent-offspring nutrient transfer in a caecilian amphibian. Boulengerula taitanus is a direct-developing, oviparous caecilian, the skin of which is transformed in brooding females to provide a rich supply of nutrients for the developing offspring. Young animals are equipped with a specialized dentition, which they use to peel and eat the outer layer of their mother's modified skin. This new form of parental care provides a plausible intermediate stage in the evolution of viviparity in caecilians. At independence, offspring of viviparous and of oviparous dermatotrophic caecilians are relatively large despite being provided with relatively little yolk. The specialized dentition of skin-feeding (dermatophagous) caecilians may constitute a preadaptation to the fetal feeding on the oviduct lining of viviparous caecilians.     

Disruptive sexual selection for plumage coloration in a passerine bird

The theory of sexual selection was developed to explain the evolution of highly exaggerated sexual ornaments. Now supported by vast empirical evidence, sexual selection is generally considered to favour individuals with the most extreme trait expression. Here we describe disruptive selection on a sexual ornament, plumage coloration, in yearling male lazuli buntings (Passerina amoena). In habitats with limited good-quality nesting cover, the dullest and the brightest yearlings were more successful in obtaining high-quality territories, pairing with females and siring offspring, than yearlings with intermediate plumage. This pattern reflects the way that territorial adult males vary levels of aggression to influence the structure of their social neighbourhood. Adult males showed less aggression towards dull yearlings than intermediate and bright ones, permitting the dull yearlings to settle on good territories nearby. Fitness comparisons based on paternity analyses showed that both the adults and dull yearlings benefited genetically from this arrangement, revealing a rare example of sexually selected male-male cooperation.     

Post-mating sexual selection increases lifetime fitness of polyandrous females in the wild

Females often mate with several males before producing offspring. Field studies of vertebrates suggest, and laboratory experiments on invertebrates confirm, that even when males provide no material benefits, polyandry can enhance offspring survival. This enhancement is widely attributed to genetic benefits that arise whenever paternity is biased towards males that sire more viable offspring. Field studies suggest that post-mating sexual selection biases fertilization towards genetically more compatible males and one controlled experiment has shown that, when females mate with close kin, polyandry reduces the relative number of inbred offspring. Another potential genetic benefit of polyandry is that it increases offspring survival because males with more competitive ejaculates sire more viable offspring. Surprisingly, however, there is no unequivocal evidence for this process. Here, by experimentally assigning mates to females, we show that polyandry greatly increases offspring survival in the Australian marsupial Antechinus stuartii. DNA profiling shows that males that gain high paternity under sperm competition sire offspring that are more viable. This beneficial effect occurs in both the laboratory and the wild. Crucially, there are no confounding non-genetic maternal effects that could arise if polyandry increases female investment in a particular reproductive event because A. stuartii is effectively semelparous. Our results therefore show that polyandry improves female lifetime fitness in nature. The threefold increase in offspring survival is not negated by a decline in maternal lifespan and is too large to be offset by an equivalent decline in the reproductive performance of surviving offspring.     

Egg investment is influenced by male attractiveness in the mallard

Why females prefer to copulate with particular males is a contentious issue. Attention is currently focused on whether females choose males on the basis of their genetic quality, in order to produce more viable offspring. Support for this hypothesis in birds has come from studies showing that preferred males tend to father offspring of better condition or with increased survivorship. Before attributing greater offspring viability to a male's heritable genetic quality, however, it is important to discount effects arising from confounding sources, including maternal effects. This has generally been addressed by comparing offspring viability from two different breeding attempts by the same female: one when offspring are sired by a preferred male, and one when offspring are sired by a less preferred male. However, here we show that individual female mallard (Anas platyrhynchos) lay larger eggs after copulating with preferred males and smaller eggs after copulating with less preferred males. As a result, females produced offspring of better body condition when paired with preferred males. After controlling for these differences in maternal investment, we found no effect of paternity on offspring condition. This shows that differences between half-sibs cannot always be attributed to paternal or maternal genetic effects.     

Post-mating clutch piracy in an amphibian

Female multiple mating and alternative mating systems can decrease the opportunity for sexual selection. Sperm competition is often the outcome of females mating with multiple males and has been observed in many animals, and alternative reproductive systems are widespread among species with external fertilization and parental care. Multiple paternity without associated complex behaviour related to mating or parental care is also seen in simultaneously spawning amphibians and fishes that release gametes into water. Here we report 'clutch piracy' in a montane population of the common frog Rana temporaria, a reproductive behaviour previously unknown in vertebrates with external fertilization. Males of this species clasp the females and the pair deposits one spherical clutch of eggs. No parental care is provided. 'Pirate' males search for freshly laid clutches, clasp them as they would do a female and fertilize the eggs that were left unfertilized by the 'parental' male. This behaviour does not seem to be size-dependent, and some males mate with a female and perform clutch piracy in the same season. Piracy affected 84% of the clutches and in some cases increased the proportion of eggs fertilized, providing direct fitness benefits both for the pirate males and the females. Sexual selection--probably caused by a strong male-biased sex ratio--occurs in this population, as indicated by size-assortative mating; however, clutch piracy may reduce its impact. This provides a good model to explore how alternative mating strategies can affect the intensity of sexual selection.     

雄激素与鼠类的社会行为

雄激素引起的社会行为包括杀婴行为、攻击行为、交配行为和社会识别行为等 ,雄激素首先引起脑结构的性差 ,是雌雄个体社会行为发生差异的基础 .雄激素引起的杀婴行为目前还有争议 ,多数学者认为还与孕酮有关 ;雄激素引起的攻击行为还受年龄、生殖状态 (泌乳时期 )、婚配制度、父本扶养还是母本扶养等各种因素的影响 ;雄激素引起的交配行为、社会识别行为还与化学感觉系统有关 ,社会识别主要由抗利尿激素依赖雄激素而产生 .     

Female sticklebacks count alleles in a strategy of sexual selection explaining MHC polymorphism.

The origin and maintenance of polymorphism in major histocompatibility complex (MHC) genes in natural populations is still unresolved. Sexual selection, frequency-dependent selection by parasites and pathogens, and heterozygote advantage have been suggested to explain the maintenance of high allele diversity at MHC genes. Here we argue that there are two (non-exclusive) strategies for MHC-related sexual selection, representing solutions to two different problems: inbreeding avoidance and parasite resistance. In species prone to inadvertent inbreeding, partners should prefer dissimilar MHC genotypes to similar ones. But if the goal is to maximize the resistance of offspring towards potential infections, the choosing sex should prefer mates with a higher diversity of MHC alleles. This latter strategy should apply when there are several MHC loci, as is the case in most vertebrates. We tested the relative importance of an 'allele counting' strategy compared to a disassortative mating strategy using wild-caught three-spined sticklebacks (Gasterosteus aculeatus) from an interconnected system of lakes. Here we show that gravid female fish preferred the odour of males with a large number of MHC class-IIB alleles to that of males with fewer alleles. Females did not prefer male genotypes dissimilar to their own.     

浅述瑶族男性成人礼仪式的基本程序

瑶族男性成人礼，是在瑶族历史长河中逐步形成的。它既是一种宗教仪式，也是对接受礼式者进行社会道德教育的一种重要形式。其实质是要代代相传，把后代培养成为具有本民族意识的能人。瑶族男性成人礼仪式的基本程序包括度戒、受戒、过法三个阶段。     

哺乳动物母体繁殖对策的研究

哺乳动物以雌体哺乳和雄性有限的 贡献共同哺育。雌体是整个繁殖过程的中心事件,也是最耗能量的过程。哺乳动物哺乳的行为表现可影响母体民仔未来的繁殖。哺乳期越长对后代越有利,但另一方面,母体的繁殖代价可影响其存活和繁殖力;后代质量与胎仔数间存在着权衡,作为胎仔数的函数,后代质量以种群新生个体补充概率潜在地影响亲本的适合度;与出生时不明确的格局相比较,育幼结束时的权衡通常非常明显;后代体重与生长速率的差异可影响新生个体的补充数;如果幼仔体重差异保持到成体,这些差异将超越简单的后代补充数而持续影响母体的广义适合度。雌性成体体重与胎仔数之间存在明显的相关性。     

Female transference and mate choice among Tana River red colobus.

Red colobus are one of a small number of primate species in which females have been reported to transfer between breeding groups more commonly than males. Several authors have hypothesised that in such species transference may serve to reduce the risk to females of producing offspring of lower fitness through inbreeding. The hypothesis offers no explanation of why females rather than males are responsible for outbreeding in these species, but remains plausible so long as male membership of breeding groups is relatively stable; for once members of one sex have evolved dispersal mechanisms reducing the risk of inbreeding, pressures on the other sex to do likewise will be lowered. Hence, if both sexes commonly migrate, the hypothesis is weakened. I describe here the membership dynamics of a group of Tana River red colobus, Colobus badius rufomitratus, which provide the first evidence of high rates of membership turnover by both sexes in primates, and speculate that the function of female transference in this case may be related to mate choice and the avoidance of infanticide.     

An extrachromosomal factor causing loss of paternal chromosomes

Extrachromosomal inheritance is ubiquitous among plants and animals; however, most extrachromosomal factors are uniparentally inherited through females, but not through males. Examples include chloroplasts, mitochondria and a variety of intracellular symbionts. The only known exception to maternal extrachromosomal inheritance in an animal is a paternally transmitted sex ratio factor (psr) which causes all-male families in the parasitic wasp, Nasonia vitripennis. Normally in this wasp, male offspring are haploid and develop from unfertilized eggs whereas females are diploid and develop from fertilized eggs. The psr factor is either a venereally transmitted infection which prevents egg fertilization (and therefore causes all-male families), or a factor transmitted to eggs by the sperm of males carrying psr, which somehow prevents incorporation of the paternal chromosomes. Here we report that sperm from psr males fertilizes eggs, but that the paternal chromosomes are subsequently condensed into a chromatin mass before the first mitotic division of the egg and do not participate in further divisions. Resulting haploid offspring are male, but have inherited the paternal factor. This extrachromosomal factor promotes its own transmission at the expense of the paternal chromosomes, and therefore can be considered a 'selfish' genetic element.     

观察箱内成年雄性布氏田鼠间的行为和行为序

研究了不同大小观察箱内布氏田鼠（Ｍｉｃｒｏｔｕｓ ｂｒａｎｄｔｉ）陌生成年雄性个体间的行为和行为序。在大，小观察箱内，除了追逐行为，优势鼠，从属鼠的行为没有明显的差别。在观察期内，虽然一对鼠中优势鼠的非社会，社会探究，攻击行为都明显地高于从属鼠，但它们在遭遇后的第１个回合的交往中，２只鼠的社会行为没有显示的区别，社会探究，争斗行为之间相互独立，为负相关关系，而其各自内部均为正相关关系，其中社会探究     

成教业余类教师权力环境要素探析

权力环境是指权力所处的社会关系。教师权力环境就是教师卖施权力时所处的社会关系。这种社会关系的主体就是教师和学生。不同类别的学生和教师构成不同的教师权力环境。成教业余类教师在把握成教业余类学生因素的基础上，还要利用好教师制度性物质资源，发展个体性物质资源，端正行使教师权力的思想动机，增强自身的人格魅力，就能取得良好的教学效果。     

Female mating bias results in conflicting sex-specific offspring fitness

Indirect-benefit models of sexual selection assert that females gain heritable offspring advantages through a mating bias for males of superior genetic quality. This has generally been tested by associating a simple morphological quality indicator (for example, bird tail length) with offspring viability. However, selection acts simultaneously on many characters, limiting the ability to detect significant associations, especially if the simple indicator is weakly correlated to male fitness. Furthermore, recent conceptual developments suggest that the benefits gained from such mating biases may be sex-specific because of sexually antagonistic genes that differentially influence male and female reproductive ability. A more suitable test of the indirect-benefit model would examine associations between an aggregate quality indicator (such as male mating success) and gender-specific adult fitness components, under the expectation that these components may trade off. Here, we show that a father's mating success in the cricket, Allonemobius socius, is positively genetically correlated with his son's mating success but negatively with his daughter's reproductive success. This provides empirical evidence that a female mating bias can result in sexually antagonistic offspring fitness.